The invention relates to a pyrotechnical gas generator.
U.S. Pat. No. 5,957,492 shows a pyrotechnical gas generator comprising a generator outer housing in which a pyrotechnical propellant charge and an igniter are accommodated, the igniter having its own self-contained igniter housing which contains a pyrotechnical material and is fastened to the generator outer housing, and the igniter housing having a base part and a cap-shaped receiving part fastened thereto. The igniter, constructed as a separate, preassembled unit, is inserted with its outer housing into an opening in a cover of the generator outer housing and is preferably fastened to the cover by means of laser welding. Laser welding, however, is very expensive as a process and is only successful when very small component tolerances are maintained. A further disadvantage of the laser welding which is provided consists in that the so-called glass/metal passage, namely the passage of electric connections through the igniter housing via openings in the igniter housing, which are potted with glass, is highly stressed thermally by the laser welding.
The solution in DE 196 01 448 A1 also has similar disadvantages, in which, however, the igniter is not constructed as a separate part with a self-contained gas-tight and moisture-tight housing, but rather in which two cup-shaped housing parts are inserted one into another and are welded to the same base. The outer housing is a part of the combustion chamber housing and the inner housing is a part of the igniter housing. The manufacture of this gas generator is costly, because the igniter is not able to be transported separately, but rather the pyrotechnical material together with the connecting lines is only filled into the corresponding receiving containers on manufacture of the entire gas generator. Therefore, also, the igniter can not be constructed as a separate supplied part.
DE 195 33 606 A1 shows a gas generator in which the base part has a radial flange which is welded to the generator outer housing. The base part has a cylindrical section, over which a receiving part is turned and is fastened to it. In this gas generator, the base part must be precisely machined at the various sections in order to permit a gas-tight welding. The welding in the region of the cylindrical section is, furthermore, provided close to the passage for the electric connections, so that the thermal stress of the material of the passage by welding is high.
The invention provides a gas generator which can be manufactured simply and in which the thermal stress of the entire igniter during welding to the generator outer housing is reduced. This is achieved in a pyrotechnical gas generator which comprises a generator outer housing in which a pyrotechnical propellant charge and an igniter are accommodated. The igniter has its own self-contained igniter housing which contains a pyrotechnical material and is fastened to the generator outer housing. The igniter housing has a base part and a cap-shaped receiving part fastened thereto. The receiving part has a radial flange with an outer edge, the outer edge projecting radially with respect to the base part and being welded to the generator outer housing. The flange is welded to the base part.
In the gas generator proposed, the receiving part has a flange which projects radially and hence acts as a heat-emitting rib, whereby the thermal stress in the region of the base part is reduced. The flange is welded on the one hand to the base part and on the other hand, in the region of its outer edge, to the generator housing. Consequently, a precise machining for welding which is to be carried out is only necessary in the region of the flange and not at several sections of the igniter housing. The receiving part therefore serves not only to accommodate the pyrotechnical material for the igniter, but also for sealing the generator outer housing, because the igniter is usually inserted into an opening in the generator outer housing.
The preferred embodiment makes provision that the base part has a radially projecting counter-flange against which the flange of the receiving part lies. The flange and the counter-flange therefore form a surrounding, radially projecting, heat-dissipating rib, which on contact with the generator outer housing makes available a large surface area for a direct heat transfer to the generator outer housing during welding.
Preferably, the welding on the outer edge of the gas generator is gas-tight and moisture-tight, so that no additional seals are provided in the region of the igniter for closing the opening in the generator outer housing.
Welding the outer edge with the generator outer housing preferably takes place by capacitor discharge welding, a welding process in which usually the two parts which are to be welded to each other are also pressed firmly against each other. Through the provision of the flange and preferably of the counter-flange, the danger does not exist that parts are deformed through the application of pressure during welding.
In addition, provision is preferably made that the outer edge lies with its entire surface against the inner face of the cover, so that the igniter housing does not project outwards with respect to the generator outer housing.